This is a practice problem about boiling point and atomic mass. The question below is asking for calculations related to the mass of each compound. For a compound to boil, the bonds within the compound have to break. The strength of the bonds, the amount of bonds, and the mass of the atoms in the compound will impact the boiling point.
To solve the problem you would first consider the atoms in the various compounds. The compounds that contain the heaviest elements will be the compounds to choose from, the other options will be eliminated. Once you have your two compounds that contain majority of the heaviest elements you can calculate their masses.
Answer choices C and D are best options in this problem because they contain elements with the heaviest masses, some math is needed to differentiate. In this case (C) is the answer, having multiple sodium and a heavy sulfur atom. Having an idea of the approximate atomic mass is essential in being able to calculate quickly. The skill also comes over time as you study the periodic table.
C) Na = 23 x 2 = 46, S = 32, O = 16 x 4 = 64
Na2SO4 = 46 + 32 + 64 = 142
D) K = 39, C = 12 x 2 = 24, H = 3 x 1 = 3, O = 16 x 2 = 32
KC2H3O2 = 39 + 24 + 3 + 32 = 98
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